Reagent for sweetening petroleum



May 2, 1933. H. H. CANNON ET AL' 1,907,150

REAGENT FOR SWEETENING PETROLEUM Original Filed Jan. 21, 1929 12 28 T p5. s;

FIG I HUGH HARLEY CANNON WRIGHT W. GARY W fiINI ENTORS M Q), AT RNEYPatented May 2, 1933 NITED STATES PATENT OFFICE HUGH HARLEY CANNON, 015LOS ANGELES, CALIFORNIA, AND WRIGHT W. GARY, OF

JERSEY CITY, NEW JERSEY, ASSIGNORS, BY MESNE ASSIGNMENTS, TO CANNON-PRUTZMAN TREATING PROCESSES, LTD., 013 LOS ANGELES, CALIFORNIA, A 003-PORATION OF CALIFORNIA REAGENT FOR SWEETENING PETROLEUM Originalapplication filed January 21, 1929, Serial No. 334,003. Divided and thisapplication filed October 21, 1929, Serial No. 401,390.

This application is a divisionof our copending application entitledContinuous method for sweetening petroleum, filed January 21,

1929, under Serial No. 334,003.

An object of our invention is to provide a method and a reagent forconverting the mercaptans or alkyl hydrosulfids which occur in petroleumdistillates into the corresponding alkyl disulfids.

A further object of our invention is to provide a method for thispurpose which is at once Cheaper and more effective than processesheretofore used.

1 A further object of our invention is to provide a method in which thechemicals applied to the oil for sweetening are continuously andspontaneously regenerated, so that their usefulness continues unimpairedfor a very' long period.

The hydrosulfids or mercaptans, having the general formula RSH, arefound in the distillates from almost all sulfur containing petroleums.The members of this roup are 2 chemically unstable, actively attaccopper and brass and have a most objectionable odor. They are thereforehighly undesirable constituents of commercial gasoline. p

The well known process of sweetening consists in converting themercaptans into the corresponding disulfids, bod es which are stable,noncorrosive and of a mild odor. As ordinarily practiced this conversion15 eflt'ected in twosteps. In the first the 01l1 treated with an aqueoussolution of lead oxld (11tharge) in caustic soda, this solutioncontaining the hypothetical sodium plumblte, a body which has nothitherto been prepared in the dry form. By this solution the mer- 49captans are converted into lead salts, the socalled lead mercaptids,which separate only slowly and incompletely from the 011. In the secondstep the lead salts are decom o sed by the addition of free sulfur, thelead eing e5 precipitated as a sulfid wh1le the two alkylsulfur radiclespreviously attached to the lead Renewed September 6, 1932.

conjoin to form the dialkyl-disulfid. The reactions which are believedto take place are as follows:

pensate, this H (RShPb (lead fier ili t iii ls iii ii-i -t sodiumhydrate) (RS): (dialkyl-disulfld) +PbS (lead sulfid) All the sulfuroriginally present in the mercaptan is also found in the disulfid andthe process is therefore not one of desulfurizat1on but is merely theconversion of a compound having deleterious properties into one Which isrelatively innocuous. It will be understood that the above remarks applyto the prior art.

As described and claimed in a companion apphcation, entitled Method ofsweetening sulfurous petroleums, filed January 21, 1929, under SerialNo. 334,004, which eventuated in Letters Patent 1,789,168, and also in acompanion application entitled Continuous method for sweeteningpetroleum, filed J anuary 21, 1929 under Serial No. 334,003, whicheventuated in Letters Patent 1,7 89 1GT we have discovered that bysubstituting calcium or other alkali earth metal for sodium in pr'eparing the lead-containing reagent, thus making (for example) a calciumplumbite instead of sodium plumbite, we gain greatly in economy andconvenience. The reagent is cheaper to make and to apply to the oil andmore readily subject to revivification, the latter advantages beingattendant on its physical condition as a dry powder rather than asolution.

In the companion application referred to, the reagent is expanded inconverting the mercaptans and, before it is reused, is subjected to anextraneous revivification step by which its usefulness is restored, at amaterial expense for the handling incident to the recovery step.

We have further discovered that if a reagent containing the same activematerials I as the reagent'just referred to (though preferably in adifferent proportion and with the addition of an inert porous body) beapplied to an oil containing mercaptans in the manner about to bedescribed,we are able to convert to the disulfid form not merely thequantity of mercaptans corresponding to the lead content in any givenquantity of the reagent, but a very much greater quantity, the reactionbeing of a continuous or cyclic nature and the active lead salt beingconstantly reconstituted as fast as it is consumed withmonoxid litharge)is prepared, this reagent tit lid

being pro ably calcium plumbite. A suitable quantity of this reagent, inpowdered form, is agitated with the oil, converting the mercaptans tolead mercaptids. Finely pulverized sulfur is then added to the oil inquantity sufiicient to precipitate the lead as a sulfid, thedialkyl-disulfids being formed by this removal of lead. The spentreagent is then separated from the oilandeither discarded or recoveredfor reuse. The reactions taking place are believed to be as follows, Rindicating any alkyl group:

Our improved continuous process consists of two stages or steps. In thefirst stage a desired quantity of the oil to be treated is agitated witha reagent similar to the above but including an amount of free sulfurcorresponding to the last equation in the above reaction, and,optionally, a small proportion of inert porous material. After avariable lapse of time the oil becomes sweet (free from mercaptans) andthe suspended powder then contains calcium hydrate, lead sulfid andprobably some unconsumed calcium plumite.

At the end of this stage, instead of separating and discarding the spentreagent we pump the oil in which it is suspended into a filter press,thus forming the spent reagent into a cake or layer on the filter cloth.We then proceed to the second stage, which consists in forcing throughthis cake further quantities of sour oil (oil containing mercaptans),adding to the stream of oil, either continuously or at intervals, suchquantity of sulfur as is required to split the mercaptid formed by thecombination of lead with the mercaptans of the 'oil. lhe oil passingthrough the nominally spent cake comes through sweet, and continues todo so for a long time thereafter; so long a time that we are uncertainas to the actual length of life of any given cake. We have 1n t i mannersweetened with a single cake up to ten times the quantity of oil whichthe amount of reagent contained in the cake would have sweetenedby thebatch process.

It is evident that in this second stage of the treatment the lead sulfidis continuously reconverted to an active form, and while we are by nomeans certain as to what chan es take place during the reaction cycle weelieve them to be as follows: p

(a) the first stage reactions are as above stated, yielding a finalreaction product containing PbS-nCa(OH) 2 (b) the second stage reactionsappear to be lPbS 26a OH) CaS+ GaO Pb+H 0 which brings us back to thestarting point and accounts for the final consumption 0' one atom ofsulfur andone molecule of calcyclic reaction is that it involves thereversible reaction Ca (UH) 3 Pb?) sCaPbO H 54 with the possibleintermediate reactions CMUH) z PbS-- Ca (OH) (SH) Plat]? The sulfurbeing loosely bonded and balancing between ibS and H 55 or CaS maybecome fired in the oil as an additional quantity of a sweet sulfid, asfor instance the disullid, and thus disappear. lhe quantity of sulfurpresent as mercaptan is usually so small that its addition to thefir-ted sulfur content of the oil is not readily determinable byanalysis.

lit should be understood that the above re actions are only tentativeand that we do not limit our invention in attempting to explain whattakes place in the second stage of the operation. l Vhatever itsmechanism may be, some regenerative reaction does take place by means ofwhich the activity and effectiveness of the reagent are maintainedthrough a long period of usefulness after the initial exhaustion in thefirst stage of the operation as above described.

In a practical way we prepare the reagent in the following manner. Wemix with water three parts of litharge with one part of commercialhydrated lime, this proportion of lime being a minimum and being bypreference materially increased. Eiuificient water lllii should be usedto produce an evenly dampened mass, though for convenience we prefer touse-a larger quantity of water, enough to bring the mass to a creamyconsistency. We also prefer to add a relatively small quantity of alight porous earth such as diatomaceous earth, this quantity beingupward from ten percent. of the weight of the other solid constituents.The addition of earth is made for the combined purpose of rendering thecake more readily permeable by the oil and of increasing the surfaceexposure of solid chemical to the oil, and should be considered asdesirable but not essential. I

The most desirable ratio of lime to lead in the mixture cannot bedefinitely fixed. The combining weights of calcium hydrate and leadmonoxid are as Ca(OH) 2 PbO 74: 223 or almost exactly one part lime tothree parts litharge. An excess of lead, while wasteful, does not impairthe efiiciency of the reagent except as regards its life. On the otherhand, there is some indication that lime is consumed during the secondstage of the treatment and in practice it appears that cakes containingan excess of lime are longer lived than such as contain an excess oflead. Inasmuch as lime is by far the cheaper ingredient we thereforeprefer to use it in material excess, and without limiting ourselves tothe proportions given, we suggest a mixture consisting of Calciumhydrate 50 parts by weight Lead monoxid 30 parts by Weight Diatomaceousearth 20 parts by weight We have, however, used mixtures ranging incomposition from ten lime ninety lead to ninety lime ten lead, with atleast moderate satisfaction in each case.

Any excess of water being removed, as by filtration, the mass is dried.Any drying means may be used and the operation may be conducted at anytemperature up to at least 300 F. Drying should be continued at least tothe point where the mass may be finely pulverized without balling orsticking. This maxi-mum will depend somewhat on the proportion of earthused. The above mixture containing 20% of earth may retain up to 45%water and still be pulverable while mixtures free from earth may requireto be dried to a maximum of 30% water. The proportion of water appearsto have no influence on the value of the reagent except as it controlsthe proportion of actual reagent in a given weight. If preferred thematerial may be rendered substantially dry, i. e., it may be dried toconstant weight at 300 F. At this point it-will retain from 1% to 4%free water. The dried material is finally ground to a fine powder, sayto pass a 150 mesh screen.

The next step in a systematic treatment is to agitate a portion of thispowder with a quantity of oil containing mercaptans, and to add a smallamount of sulfur either to the powder or to the oil. The point at whichthis addition is made appears to be a matter of no consequence; thesulfur may be added to the powder before it is mixed with the oil, orthe addition may be made to the oil immediately after the powder isintermixed or some time thereafter. The reagent does not reach its fullreactivity with mercaptans until some time after the sulfur is added,and it is probably desirable to add the sulfur either with the powder oralmost immediately after it is mixed with the oil. The sulfur should notbe added to the mixture before drying, as this will result in theproduction of an inactive form of lead sulfid.

The proportion of reagent powder to oil to be taken for this initialstep is limited in one direction onlyit must be sufficient to sweetenthe quantity of oil taken, but may be much greater if preferred. Suchquantity of reagent should be taken as will, produce a cake ofthe'desired thickness in the particular filter press to be used. Thisthickness may be governed by three considerations. The thicker the cakethe more rapidly may the sour oil be passed through it While allowingsufficient time of contact. Again, the thicker the cake the more reagentwill it contain per unit of area and thus, assuming a c0nsum p tion ofone of the ingredients of the cake, the longer will be its life. On theother hand, the thicker the cake the greater will be the resistance tothe flow of oil through it. We have found in practice that the cakeshould not be much thinner than one-fourth inch and that it may be up tofour times this thickness without setting up a serious back pressure. Aquarter inch cake is capable of converting an extremely sour oil(testing 33% with standard sodium hypochlorite solution) at a flow rateof from 12 to 25 gallons per hour, and a faintly sour oil (testing 1%pyro solution) at a rate of from 100 to 250 gallons. At these rates thepressure is low.

After a suflicient time of agitation, which may be a few minutes orseveral hours, the oil becomes sweet and the reagent changes in colorfrom White to blackish-gray, due to the formation of lead sulfid. Theoil is now pumped through a filter press, the reagent collecting on thecloths to form a thin layer or cake. Care should be taken to distributethe reagent evenly on the cloths, avoiding thin spots, and it isdesirable to use a type of press and a pump arrangement such as willpermit circulation through the press in order to keep the heavy reagentfrom settling out before it reaches its destined position on the cloth.

For this purpose the simple arrangement shown in the attached drawing issuggested. In this drawing Fig. 1 illustrates in a highly diagrammaticmanner an arrangement of press, agitating tank and filter which issuitciently to place able for the carrying out of our method invention.In the figure, 11 is a steel agitator or feed tank provided with aclosed top 12 and a hinged manhole plate 13 for the introduction of drypowder.

The tank has a conical bottom 14, the point of which communicatesthrough pipe 15 with a pump 16, which may be of centrifugal, rotary orother preferred type, driven by means not shown. The discharge 17 ofthis pump branches into two pipes; 18 which communicates with the top ofthe filter 19 and is controlled by valve 20, and 21 which communicateswith the top of tank 11 and is controlled by valve 22. The filterconsists of an outer shell 23 and an inner supporting tube 24:, whichmay be of stiff wire screen or other material which will afford supportto a tube 25 of cotton or other filter cloth and which will permit freepassage to such liquid as passes through the cloth. The outer shell isprovided at the bottom with a drain pipe 26 controlled by valve 27, forcarrying away sweetened oil, and at or near the top with an inlet pipe28 controlled by valve 29, for the introduction into the shell of air orother fluid under pressure. The lower end of the tube communicates withthe top of tank 11 through pipe 30 controlled by valve 31. A pipe 32controlled by valve 33 affords com-. munication between the tank and asource of supply of sour oil. A branch pipe 34: controlled by valve 35affords communication between the sweet oil drain 26 and the top of tank11.

To perform the operations already described, tank 11 is filled to adesired level with sour oil by opening valve 33, which is closed whensuch level is reached. The pump 16 is then put into operation, valve 22being open and valve 20 closed, thus circulating the oil from the bottomof the tank back into its top. The re uired charge of powder is thenintroduce into the tank through manhole 13 and the necessary amount ofsulfur shortly thereafter, care being taken to make these additionsgradually so as not to choke the pump. Circulation is then continueduntil the powder is evenly diffused through the oil and as longthereafter as may be required to produce the above described reactionbetween the powder and the oil and to sweeten the 011 contained in thetank.

Valve 20 is now opened and valve 22 closed, thus diverting the pumpdischar e into the press. At this time valve 29 on t e air inlet shouldbe closed, valve 27 on the sweet oil drain open and valve 31 choked downsufiithe desired pressure on the ress. The delivery of the pump shouldbe such that at least twice as much oil will enter the press throughpipe 18 as can pass through the cloth 25 and the supporting tube 24 tothe sweet oil drain 26, and it is better to have not less thanthree-quarters of thepump delivery leave the press and return to theagitating tank through the pipe 30. This ensures for formation of aneven layer on the cloths by keeping the reagent in suspension. Ifnecessary the delivery of the press, during the cake forming stage, maybe reduced by partially closing valve 27.

In place of the continued agitation above described the cake may beformed in the press immediately after adding the sulfur and the oil thencirculated repeatedly through the cake until the sulfid forms in thecake and the oil becomes sweet. To obtain this circulation valve 27 isclosed and valve 35 opened or partially opened, thus permitting thepress effluent to flow ject of either procedure is merely to maintaincontact between the oil and the reagent until these changes occur.

The cake having been formed and activated in either manner, valve 35 (ifopen) is closed, valve 27 opened and the sweetened oil discharged to asuitable tank not shown, and valve 32 opened to a sufficient degree tomaintain the desired level in tank 11 by replacing the oil withdrawnthrough the press. At the same time valves 27 and31 should be regulatedto pass the oil through the press at such rate that it will come throughperfectly sweet. This feeding of sour oil into the tank and withdrawalof sweet oil from the press, with the addition to tank 11 from time totime of small quantities of sulfur, may now be continued until the rateof delivery from the press falls below a desired minimum rate, becauseof decreased permeability of the cake, or until the oil fails to comethrou h sweet at this minimum speed, because of epreciation of thechemical constituents of the cake.

The proportion of sulfur to be added with the sour oil as fed and theproportion which should be added to the original batch may readily bedetermined if the percentage of sulfur existing as mercaptan in the souroil is known. It will be seen from the equations above that the addedsulfur should be just one half the mercaptan sulfur. If this proportionis not known the effluent from the press may be sampled from time totime and tested. If the oil reacts sour in the well known doctor testthe proportion of sulfur being added is to small, while if the oil givesa positive indication in the corrosion test the proportion is too large.Because of its tendency to render the oil corrosive the addition of anymaterial excess of sulfur must be avoided. It is not necessary to feedthe sulfur continuously; if the oil is being fed from a tank such asthat shown in the figure the quantity of sulfur required for the entirecharge may be added to the oil at once, or if it is being fed in astream from such source that the sulfur cannot be added to a body of theoil, the sulfur may be injected into the stream in small quantities atback into tank 11. The ob- I I A frequent intervals. A suspension of thefinely ground sulfur in a small quantity of oil may conveniently be usedfor feeding into the stream, as by means of a minute pump synchronizedwith a meter on the oil line.

We have noted that in the long continued use of a single dose of reagentthe proportion of sulfur required to produce a sweet oil graduallydiminishes and becomes less than the calculated quantity. The reason forthis we do not know, but the observation is importantas it indicatesthat too much dependence should not be placed on a calculation of theproportion of sulfur required, but that the stream of oil should fromtime to time be tested, not only for sweetness but also for itscorrosive properties, in order that the continuous addition of an excessof free sulfur ma be avoided.

fter the passa e of a large quantity of oil through a sing e cake therate of flow is liable to fall below a commercially satisfactory rate.The cake becomes denser and offers more resistance to the passage of theoil. This increase in density is undoubtedly due in part to a merephysical settling and packing of the particles of which the cake iscomposed, but we believe it to be due in part to the removal of leadplumbite from the interior of the cake and the redeposition of the leadas a finely divided lead sulfid on its intake face. Whatever the reason,the difliculty may be overcome and the original flow rate reestablishedby breaking down the cake and remixing it with the oil contained in tank11. -To accomplish this we fully open valve 31, valve 22 being closed,and also close valve 27, thus stopping the filtering action and raisinthe flow of oil through tube 25 to the big est velocity. We thenpartially open valve 29 and introduce into the shell 23 a fluid underpressure, such fluid for instance being air or sweetened oil. This fluidpressure, coming onto the reverse side of the cloth 25, breaks anddislodges the cake, which is swept forward by the velocity of the oilstream through pipe 30 and thus back to the tank. A few minutescirculation will completely diffuse the cake material in the oil, afterwhicha new cake may be built up as previously described. This cake willbe found to have substantially the original permeability and flow rate.

The quantit of oil which may thus be sweetened wit a single charge ofthe reagent chemical is very great, but the exact life of the reagent isnot known and is' undoubtedly variable. We have observed that after longcontinued use the activity of the reagent diminishes, and that theactivity may be reestablished by the addition of small quantities oflead monoxid. It is probable, though not certain, that there is someconversion of lime into the sulfid, but the rate of consumption is soexceedingly low that it is not likely that this is a determining factorin the cally there is no consumption of lead but in practice it doesdisappear very slowly, probably minute quantities are carried away inthe sweetened oil in the form of lead mercaptid. Certainly some of thelead is precipitated on the walls of the apparatus and connecting pipesin the form of lead sulfid, and in puttlng new apparatus into operationthis may cause the withdrawal from the cycle of a material quantity oflead until such time as all crevices and areas of low velocity arefilled and coated. At the worst the loss of lead in either manner isminute as com ared with the consumfption of this element 1n theprocesses hereto ore used, and by replacing this small loss the reagentmay be maintained in effective form indefinitely, so far as we presentlyknow.

While we have described the application of oil and'sulfur to-the reagentin a filter press we would have it understood that our invention is notlimited to this particular manlpulation. We may form the reagent into apack on trays or in the bottom of a percolator and pass the oil throughthis pack by gravity or underpressure, or we may utilize the well knowncounterflow thickening apparatus in which the reagent carried forward insuspension is continuously returned to the first contacting vessel, orwe may even work 1n a semi-continuous manner, separating the reagentfrom the sweetened oil, returning it with the required sulfur to a batchof sour oil, intermixing until the oil is sweetened and the reagentactivated, and separating the reagent to be applied to another batch ofoil, and so on seriatum. These various methods differ only as toconvenience, the final result in each case being the samethe contactingof progressive quantities of sour oil with unit quantities of reagent,which reagent is maintained in active condition by the addition of freesulfur in quantities proportionate to the quantity of oil passingthrough the contacting system.

We would also have it understood that while we have, to avoid constantrepetition, referred to the use of calcium hydrate, substantially thesame results may be had in substituting, wholly or in part, hydroxide ofany of the metals in group 2 of the periodic system, and in particularthe hydroxide of barium, strontium, magnesium and zinc.

Where, in the above specification and the attached claims, we refer tosour oil, we would be understood to mean a petroleum product which onagitation with an aqueous solution of litharge in caustic soda (the wellknown doctor solution) and the addition of a small quantity of freesulfur, gives a discoloration due to the formation of lead sulfid, suchoil being considered to contain mercaptans or alkyl hydrosulfids. Whenwe refer life of the reagent. Theoreti-' to a sweet oil we would beunderstood to refer to a petroleum product which gives a negativeindication to such test, and which is substantially free from theaforesaid mercaptans, though it may and usually does contain sulfur inother combinations.

We claim as our invention:

1. A reagent for directly converting mercaptans into alkyl clisulfids,comprising calcium hydrate, lead monoxid and free sulfur.

2. A reagent for directly converting mercaptans into alkyl disulfids,comprising calcium hydrate, lead monoxid, a light porous nonreactivematerial and free sulfur.

3. A reagent for directly converting mercaptans into alkyl disulfids,comprising a hydrate of a metal of the second group of the periodictable, lead monoxid and free sulfur.

4. A reagent for directly converting mercaptans into alkyl disulfids,comprising a hydrate of a metal of the second group of the periodictable, lead monoxid, a light porous nonreactive material and freesulfur.

5. A reagent for treating oils containing mercaptans, comprising:calcium hydrate, lead monoxid and a light, porous nonreactive material.

6. A reagent for treating oils containing mercaptans, comprising ahydrate of a metal of the second group of the periodic table, leadmonoxid and a light, porous, nonreactive material.

In witness that We claim the foregoing we have hereunto subscribed ournames this 16th day of October, 1929.

HUGH HARLEY CANNON. WRIGHT W. GARY.

